The SS114 is a "Standard" seat which has a flat back. It looks like a regular seat but is a "Softclose".
The SS204 is a "Oval" seat, so it is round in the back. This seat looks good on the Aquia, Nexus, Mercer... any toilet that has a oval look to it.
I have heard of some seats wobbling what usually happens is when someone is wiping that person will sit and push the seat more on one side and it will loosen over time because the bolts and nuts are plastic.
The Aquia comes with top mounted bolts which are a brass bolt and a rubber anchor. So it will be better than the plastic bolts and should stop it from coming loose.